Loudspeakers as electro-acoustic converters, are in known in a great variety (as for power and frequency range). As a speaker with only one diaphragm is not suitable for providing full performance over the whole audible frequency range, in order to provide better acoustic performance, more, preferably two (high- and low-range) or three (high-middle and low-range) speakers are combined in a speaker system, which can be connected to an output of an acoustic power amplifier via a two- or three-way crossover. Generally, speaker systems with multiple speakers of that kind can only be mounted into relatively large speaker boxes.
In order to reduce the required space and thus the size of such a loudspeaker box, a solution is provided by a coaxial arrangement of the different speakers in a common frame. Current loudspeakers of car radios and of car amplifiers have generally coaxial arrangement, providing a relatively wide audio frequency range with little space requirement. Due to the smaller size, the loudspeakers with coaxial configuration have less power output, e.g. the current load capacity is more limited when compared to multi-speaker systems of larger size. Higher voltage- or current load in such conventional multi-speaker systems will lead to higher distortion and shorter life time.
Patent document DE19913558 discloses a coaxial loudspeaker, in which between the voice coil of the outer subwoofer diaphragm and the voice coil of the inner tweeter diaphragm, there is only a single common magnetic circuit between ferrite cores. The loudspeaker is small in size and weight, but it is not suitable to provide higher power audio output. A further problem arises from the fact that both of the diaphragm voice coils move in a magnetic field of substantially the same strength, which, without appropriate frequency dependent compensation, would cause distortion.
U.S. Pat. Nos. 6,963,650 and 4,821,331 disclose coaxial loudspeakers, in which the voice coil of the subwoofer diaphragm and the voice coil of the tweeter diaphragm are located in two different magnetic circuits, between ferrite cores. These solutions provide for the possibility to control the different voice coils in magnetic fields of different strength, but the arrangement of the two diaphragms in two planes above each other leads to a difficult construction and to a higher weight.
Therefore, it is an object of the present invention to provide a coaxially arranged loudspeaker, which has a relatively small size at a high audio power output, a wide audio frequency band and a high current load capacity. It is a further aim of the present invention to provide a coaxial loudspeaker arrangement with a low distortion and a longer life time even at higher power output in contrast to similar loudspeakers known from the prior art.